The disclosure relates generally to distribution of power to one or more power consuming devices over power wiring, and more particularly to distribution of lower voltage power to remote communications devices in a distributed communications systems (DCS), such as distributed antenna systems (DAS) for example, for operation of power consuming components of the remote units.
Wireless customers are increasingly demanding wireless communications services, such as cellular communications services and Wi-Fi services. Thus, small cells, and more recently Wi-Fi services, are being deployed indoors. At the same time, some wireless customers use their wireless communication devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of distributed antenna systems (DASs). DASs include remote antenna units (RAUs) configured to receive and transmit communications signals to client devices within the antenna range of the RAUs. DASs can be particularly useful when deployed inside buildings or other indoor environments where the wireless communication devices may not otherwise be able to effectively receive radio frequency (RF) signals from a source.
In this regard, FIG. 1 illustrates a wireless distributed communications system (WDCS) 100 that is configured to distribute communications services to remote coverage areas 102(1)-102(N), where ‘N’ is the number of remote coverage areas. The WDCS 100 in FIG. 1 is provided in the form of a DAS 104. The DAS 104 can be configured to support a variety of communications services that can include cellular communications services, wireless communications services, such as RF identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), and wireless LAN (WLAN), wireless solutions (Bluetooth, Wi-Fi Global Positioning System (GPS) signal-based, and others) for location-based services, and combinations thereof, as examples. The remote coverage areas 102(1)-102(N) are created by and centered on RAUs 106(1)-106(N) connected to a central unit 108 (e.g., a head-end controller, a central unit, or a head-end unit). The central unit 108 may be communicatively coupled to a source transceiver 110, such as for example, a base transceiver station (BTS) or a baseband unit (BBU). In this regard, the central unit 108 receives downlink communications signals 112D from the source transceiver 110 to be distributed to the RAUs 106(1)-106(N). The downlink communications signals 112D can include data communications signals and/or communication signaling signals, as examples. The central unit 108 is configured with filtering circuits and/or other signal processing circuits that are configured to support a specific number of communications services in a particular frequency bandwidth (i.e., frequency communications bands). The downlink communications signals 112D are communicated by the central unit 108 over a communications link 114 over their frequency to the RAUs 106(1)-106(N).
With continuing reference to FIG. 1, the RAUs 106(1)-106(N) are configured to receive the downlink communications signals 112D from the central unit 108 over the communications link 114. The downlink communications signals 112D are configured to be distributed to the respective remote coverage areas 102(1)-102(N) of the RAUs 106(1)-106(N). The RAUs 106(1)-106(N) are also configured with filters and other signal processing circuits that are configured to support all or a subset of the specific communications services (i.e., frequency communications bands) supported by the central unit 108. In a non-limiting example, the communications link 114 may be a wired communications link, a wireless communications link, or an optical fiber-based communications link. Each of the RAUs 106(1)-106(N) may include an RF transmitter/receiver 116(1)-116(N) and a respective antenna 118(1)-118(N) operably connected to the RF transmitter/receiver 116(1)-116(N) to wirelessly distribute the communications services to user equipment (UE) 120 within the respective remote coverage areas 102(1)-102(N). The RAUs 106(1)-106(N) are also configured to receive uplink communications signals 112U from the UE 120 in the respective remote coverage areas 102(1)-102(N) to be distributed to the source transceiver 110.
Because the RAUs 106(1)-106(N) include components that require power to operate, such as the RF transmitter/receivers 116(1)-116(N) for example, it is necessary to supply power to the RAUs 106(1)-106(N). In one example, the RAUs 106(1)-106(N) may receive power from a local power source. In another example, the RAUs 106(1)-106(N) may be powered remotely from a remote power source(s). For example, the central unit 108 may include or be coupled a power source 122 and configured to remotely distribute power over cables that carry the communications links 114 to the RAUs 106(1)-106(N). For example, the communications links 114 may be cables that include electrical conductors for carrying current (e.g., direct current (DC)) to the RAUs 106(1)-106(N). If the WDCS 100 is an optical fiber-based WDCS in which the communications links 114 include optical fibers, the communications links 114 may by a “hybrid” cable that includes optical fibers for carrying the downlink and uplink communications signals 112D, 112U and separate electrical conductors for carrying current to the RAUs 106(1)-106(N). Examples for low power delivery over communication lines are: Telephony lines that are used to carry xDSL modem (Digital) with voice (Analog) signals together with power, or alternatively Power over Ethernet (PoE) which carries power and Ethernet over CATS or CAT6 wire cables.
Some regulations, such as IEC 60950-21, may limit the amount of direct current (DC) that is remotely delivered by the power source 122 over the communications links 114 to less than the amount needed to power the RAUs 106(1)-106(N) during peak power consumption periods for safety reasons, such as in the event a human contacts the wire. One solution to remote power distribution limitations is to employ multiple conductors and split current from the power source 122 over the multiple conductors, such that the current on any one electrical conductor is below the regulated limit. Another solution includes delivering remote power at a higher voltage so that a lower current can be distributed at the same power level. For example, assume that 300 Watts of power is to be supplied to a RAU 106(1)-106(N) by the power source 122 through a communications link 114. If the voltage of the power source 122 is 60 Volts (V), the current will be 5 Amperes (A) (i.e., 300 W/60 V). However, if a 400 Volt power source 122 is used, then the current flowing through the wires will be 0.75 A. However, delivering high voltage through electrical conductors may be further regulated to prevent an undesired current from flowing through a human in the event that a human contacts the electrical conductor. Thus, these safety measures may require other protections, such as the use of protection conduits, which may make installations more difficult and add cost.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.